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26 December 2015

Airworthiness Directive for A350: failures on inboard aileron EHAs.

The European
Aviation Safety Agency (EASA) is giving operators of the Airbus
A350 until 11/Jan to begin daily post-flight checks of the aircraft’s 2 inboard
ailerons to verify that the electro-hydrostatic actuators (EHAs) that drive the
roll-control surfaces are working properly.

The AD (Airworthiness
Directive) issued by EASA requires repetitive post-flight checks (activation)
of each inboard aileron EHA and, in case of failure, replacement of the
affected EHA with a serviceable one.

The interim
action required by the AD (Airworthiness Directive) specifies that since 28/Dec
until 11/Jan and, thereafter, during each flight day, but not exceeding 2
flight cycles, it is needed to accomplish a post-flight activation procedure on
each inboard aileron EHA in accordance with the instructions of Airbus AOT
A27P007-15-00.

Source: Moog

If, during
any EHA activation the message “F/CTL INR AILERON ELEC ACTUATOR” is triggered,
before next flight, it will be mandatory to accomplish the troubleshooting
procedure on the affected EHA in accordance with the instructions of Airbus AOT
A27P007-15-00.

If the
failure remains, before next flight, it will be needed to replace the affected
EHA with a serviceable one.

Further
analysis and testing by Airbus determined that in such cases the switch from
damping to active mode did not occur, preventing the activation of the EHA.

This failure
corresponds to a scenario called ‘’spurious damping’’ and can be detected only
when the EHA is activated.

As a
consequence, the EHA will not be able to take over in case of adjacent servo
control failure or yellow hydraulic failure.

This
condition, if not detected and corrected, and combined with other failures could result in loss of control of inboard
aileron potentially resulting in inability to ensure sufficient control on
the roll axis of the aeroplane.